In the manga Mudazumo Naki Kaikaku, the protagonist Junichiro Koizumi is able to use "goumoupai", the ability to turn any mahjong tile into a white/haku tile simply by gripping it with immense strength, usually leaving the tile dented.

Sure, the manga frequently goes overboard with the abilities of each character, but this one seems like it might actually be possible in real life. I'd assume that the material the tile is made out of would be a giant factor, but apparently Koizumi can even do it with depleted uranium tiles.

How much grip force would be needed to scrape/dent a mahjong tile so that it turns white? Would it be possible for a human (for any material)?

  • 1
    Umm, isn't it more suitable to be posted on Physics even if it's related to anime/manga? Related meta post on there, though. Btw, good question though.
    – Aki Tanaka
    Apr 1, 2015 at 6:32
  • @Aki Sorry, new to the site so I wasn't sure what was in scope or not (I assumed it was okay because there's also the railgun question). I'd be okay with deleting if necessary.
    – Sp3000
    Apr 1, 2015 at 6:52
  • No problem. Personally, I don't have any problem with this being posted here, though I think the question is more related to physics, so no need to delete it :)
    – Aki Tanaka
    Apr 1, 2015 at 7:49

1 Answer 1


The average human hand cannot produce enough grip force to do such a thing. In this study on grip strength, the maximum key grip (holding an object like you would a key) force listed is 42 pounds.

Wood will probably be the softest material a typical modern mahjong tile is made of, from the link in your post. Looking at the compression strength properties of wood, the softest wood listed compresses at 193 pounds per square inch. Keep in mind that hardwoods like maple (456 psi) or oak (778 psi) would actually be used rather than softwoods.

Plastics take things to an entirely new level. This chart shows the compressive properties of some common polymer plastics. Note that the values are given in MPa, or megapascals. 1 megapascal = 145.037738 pound-force/square inch (PSI).

As for materials such as pulverized bone, the only references I could find involved using the materials as partial replacement for concrete. I'd say it's safe to infer that the compressive strength for the compound used in making mahjong tiles would be at least as strong as hardwoods.

Keep in mind these figures only talk about the compression strength of the material. Just compressing the tile alone would not be enough to remove the engraving and paint of the characters on the tile face. Some shear force would also need to be applied as well. I don't think it's necessary to go there at this point, though.

  • I thought wood might at least be doable, but I guess it's impossible after all. Thanks for the well-researched answer.
    – Sp3000
    Apr 6, 2015 at 4:47

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